Water heater t&p valve replaced still leaking

Hi...

Here's my problem that I hope someone can lend some insight into. I have a Rheem 40 Gal gas water heater. The other day, the T&P valve started dripping only when the tank was heating and a little while afterwards. About enought to fill a juice glass. I had the T&P valve replaced, it worked properly when the plumber was there; thought all was fine. That night, started back to dripping. Plumber came back and thought maybe it was a bad T&P and made a 2nd replacement. This didn't help. And the water coming out of the pipe is cold water not hot water. He has measured the pressure inside at the shower head and outside at the faucets and all is normal. When the water heater is not in the heating mode, the pressure (measured on the water heater outlet where you can hook a hose to) is within limits, once the burners came on, the pressure rose and eventually tripped the t&p valve (this time hot water).
After 5 hours...we were to the point that the temperature is fine but the pressure is what is causing the release of water. The next step was the pressure regulation valve...we couldn't find one. The plumber wants to check to see if it has gone bad and letting too much pressure into the tank. I've contacted the builder to get blueprints of the plumbing system to find out where it is. I'm reading other posts where people are taking about the expansion tank, could this be the problem. After the blueprints come in, the plumber is coming back to check the regulation valve (even though the code says it should be visible, we can't find one...if it was placed in the wall, we will have to cut a hole in the sheetrock). I'm wondering if it sounds like the expansion tank has gone bad, that may save some effort. Any advice is appreciated.

Expansion tank time.

What can I say? Sounds like expansion tank time.

If you have a PRV in the system, you need an expansion tank.

However, many water districts are adding check valves at the water meter, and when they do.........you have to install an expansion tank.

[FONT=Arial, Helvetica, sans-serif]Thermal expansion occurs when water is heated during non-use periods. The installation of a Pressure Reducing Valve (PRV), Check Valve or Back Flow Preventer "closes" the water system, leaving water with no room for expansion. Many local codes now require a closed system, to prevent backflow into the water main. [/FONT]

Good luck finding "blueprints" of the plumbing system.

Neither the PRV or the expansion tank, if they exist, should be hidden out of sight. Do you have a utility room, or a basement area where water enters the house? Exp.tank often located near WH for convenience, but could be anywhere inside the house.

thanks for the input

Hi...thanks for the posts...I do have an expansion tank and it is located with the water heater...just don't know if that is the problem or not...my plumber is thinking the prv valve...I know this sounds odd...but we can't find it...my house is on a concrete slab..I don't have a storage closet nor a garage. We can see which line coming into the water heater closet is the one from the city. It comes out of the wall and goes back in. We called the company that "bought" the company that built my house and they said they can order the blueprints for the plumbing system. They couldn't find anyone in their office that was involved in building my neighborhood. I honestly think that somehow it was sheetrocked over...I guess if it is, and we have to bust a hole in it...I guess it would help for future problems in terms of access. I'm supposed to have an answer Friday on the location of the prv valve from the building company.

My water heater is in a closet in the kitchen, I wouldn't be so concerned about the leakage except it really has no where to go except onto the floor. For the time being, I have a drinking glass under the pipe to catch the water. There's no way to vent it outside. The closet is not on an outside wall. It's not a lot of water...just enough to fluster me.

Just concerned that we may be replacing parts that are not problematic only to wind up costing lots of money.

The plumber says this is the oddest situation he has seen. First, surprised that the water coming out of the t&p pipe is cold, and secondly, that we can't find the prv valve.

Thanks again for the information..i'll keep everyone updated on my saga as it continues.

Rap on the expansion tank to try to determine if it is full of water. It should not be! If it is, it either does not have any air pressure in the dry side, is very low pressure, or has failed. When they installed one on my heating system (same concept), they put a shutoff valve on the t connection (it makes it easier to replace!). If you have one, make sure that it is open.

still working on the problem

thanks everyone for the posts...i've tapped on the expansion tank and really can't tell a difference in the sound at the top of the tank as oppossed to the bottom...i'm being told the blueprints will be in today for the plumbing system....just received a call from the builder...they said it is there above the main cutoff...told them its not...they sent their representative out and I just got back...there is NO prv valve...he couldn't see one in the pictures i took of the house when it was being built...they can't say how it passed inspection without one....they are calling the plumbing company that originally installed the plumbing to come out and install one...hoping that will take care of the problem...i'll keep everyone informed...

Prv

The simple answer is that if you do not have a PRV, you would not have the problem, unless there is also a check valve installed somewhere that is preventing the pressure equalization.

In my limited experience, it is pretty easy to tell the wet side from the dry side of an expansion tank. If it sounds dull when you hit it on either end, then the bladder is probably shot. If it sounds hollow on each end (not likely), then maybe the air pressure is set way high.

Deb

Ummmmmm
Has anyone actually checked the incoming pressure? You may not have a PRV, you may not need one. Has anyone called the water company? You may have a check valve installed by your water company at the meter (as Terry and hj mentioned earlier). All closed systems need expansion tanks. Most expansion tanks have an air valve that you can check. The bladder could be ruptured or it could have lost air over time. It kind of seems to me that this is getting a little overcomplicated--there are alot of simple things that could be checked (and most likely solved) while you were waiting for blueprints (that are very often wrong, as you discovered).
Deb
The Pipewench

problem finally solved !

Hey to everyone and thanks for the posts....! I think my problem has been solved...the original plumbing company came out this morning and installed the prv valve....(so at least my house now meets city codes)....kept my fingers crossed when we turned everything back on...only to feel my heart hit the floor when the water started dripping again...IT WAS THE EXPANSION TANK ALL THE TIME....the plumber had to run to another job but came back at lunchtime with a new expansion tank....once he unscrewed the old one...it was so full of water, it was an effort to lift it and move it to the sink to drain...and it all makes sense to me that the other day I used my tire pressure gauge on it and it didn't register anything...needless to say, he had to head out, but I stayed and waited for the water heater to heat up and cut off...then I turned on the tub faucet to just use up the hot water to the point of the water heating kicking back on...so far, twice with no leaks....I had to of course pay for the t&P valve replacement last week, the prv valve was on the plumbing company for not installing one in the first place when the house was built, and the expansion tank was on me...as long as its not leaking when I get home tonight...I will be happy...it was also nice to have a plumber (today) that listened to my concerns and questions and explained things to me...I will definately use them again. Thanks again to everyone for the posts and the advice...it did come in handy.

Scott